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Frequency
Sfandard Calibration
5.18
The
'cycle
drift'
method
of
frequency
calibration,
described below,
is
suitable
^
for oscillators
which have
temperature
stability characteristics
of
up
to
1
part
in
10
.
The higher
stability oscillators,
such as
the
Racal
9421
and
9442,
require
specialised
equipment
such
as the Tracor
Frequency
Difference
Meter
Type
527A,
if
the
optimum
calibration
is
to
be achieved.
5.19
Equipment
Required
Oscilloscope.
1
MHz
external
frequency
standard, with
accuracy
better than
one
part
in
10^.
5.20
Procedure
(1)
Allow
a
suitable
warm—up
period
(not
less
than
one
hour
for
a temperature
controlled
oscillator).
(2)
Set the oscilloscope time base
to
1
ps/cm.
(3)
Connect
the
1
MHz
external standard
to
the 'External
Trigger'
input
of
the oscilloscope.
(4)
Connect
the
oscilloscope lead
to
the
inner pin of the
'1
MHz
OUTPUT'
socket
on
the rear
panel (Screen
to
chassis).
(5)
Observe
the
oscilloscope display
and check
that
in
a period of 10 seconds
not
more
than
one
cycle
of displayed
waveform moves
past
a fixed point
on
the oscilloscope face.
(6)
If
necessary, adjust
the oscillator
trimmer
to
obtain a
stationary trace.
The
trimmer
is
accessible via
an
aperture
in
the rear
panel,
except
for
a
few
early
models
in
which
the standard oscillator
is
mounted on
the
main
p.c.b.
9901
Vol.2
5-11
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